Pneumatic conveying system



Sept. 7, 1954 A. o. RIORDAN PNEUMATIC CONVEYING SYSTEM Filed June 5, 1952 4 Sheets-Sheet 1 f'eillfrt Candy M6 VM Sept 7, 1954 A. o. RIORDAN 2,688,517

PNEUMATIC CONVEYING SYSTEM Filed June 5, 1952 4 Sheets-Sheet IS (Sia,

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SCP- 7, 1954 A. o. RIORDAN 2,688,517

PNEUMATIC CONVEYING SYSTEM Filed June 5, 1952 4 Sheets-Sheet 4 All 2;/ iff 2.54 215 IN V EN TOR.

E. E, fig/erf 0. Fla/'414m Patented Sept. '1, 195,4v

PNEUMATIC CONVEYING SYSTEM Albert 0. Riordan, Saginaw, Mich., assignor to Baker Perkins Inc., Saginaw, Mich., a corporation of New York Application June 5, 1952, Serial No. 291,837

(Cl. 3D2-28) 13 Claims. 1

The present invention relates to pneumatic conveying systems and particularly to systems adapted for use in conveying flour in bakeries, Where it is necessary to convey a xed weight of our from a bin to a mixer at frequent intervals to produce batches of bread dough.

It has been proposed that a previously weighed quantity of flour be fed into a pneumatic conveyer and delivered by the conveyer to a mixer located at a more or less remote point. See, for example, the patents to Hicks No. 1,256,017, Lauterbur et al. No. 2,003,716 and Israel No. 2,572,862. An objection to that type of system lies in the fact that it is necessary to separate all of the flour from the conveying air at the mixer to avoid delivering a short weight. Since commercial flour contains a substantial percentage of nes which oat easily in almost still air, it is necessary to employ in the previously proposed systems a large and expensive separator at the mixer.

In prior nonpneumatic bakery conveying systems, it has been common practice to position a weighing scale over the mixer. The conveyer, usually of the screw type, delivers flour to the scale hopper until the scale beam tips and automatically stops the conveyer. The flour then is dumped by gravity from the scale hopper into the mixer. However, this arrangement of a scale hopper over the mixer cannot be used with any prior pneumatic conveying systems for several reasons. In the rst place, most bakery buildings do not have suiiicient headroom to permit the positioning of both a scale hopper and a standard cyclone separator, one above the other and both above a mixer. More important, it is not possible to stop any of the prior pneumatic conveyers when the scale hopper has received the desired amount of flour because the flour in the line between the storage bin and the separator over the scale hopper would drop out of suspension and clog the line as soon as flow ceased. Any time a pneumatic flour conveyer is stopped with our in the line, it becomes so clogged that all of the conveyer pipes must be taken down and cleaned out. To stop the conveyer, it is necessary to stop the feed of flour to the conveyer intake and continue the flow of air until the line is cleared of our. It is not possible to estimate with the requisite degree of accuracy the amount of flour in the line and allow for that amount in the scale beam setting. Moreover, in many cases a mixer may draw flour from any one of several bins located at different distances from the mixer and the quantity of flow in the line will be different in each case.

It is the general object of this invention to provide an improved, simplified and relatively inexpensive pneumatic conveying system for conveying material, such as flour, to a desired destination from a larger quantity in a bin or other storage chamber.

More particularly, it is an object of this invention to provide a conveying system of the type mentioned which is peculiarly suited for use in conveying flour to the dough mixer or mixers in a commercial bakery in that the mixer at the desired destination receives only a predetermined Weight of ilour.

Another object of the invention is to provide a system of the type mentioned in which it is not necessary to employ large and expensive cyclone separators.

A further object of the invention is to provide a system of the type mentioned capable of delivering flour to any one of a plurality of destinations from a single source or from any one of a plurality of sources.

Another object of the invention is to provide an improved and simplified electrical control circuit for such systems.

Other objects and advantages of the invention will become apparent from the following specication, the accompanying drawings, and the appended claims.

In the drawings:

Figure 1 is a diagrammatic illustration of an elementary form of the invention;

Figure 2 is a sectional view showing the construction of one of the conveyer line valves employed;

Figure 3 is a diagram of an electrical control circuit for the system shown in Figure l;

Figure 4 is a diagrammatic illustration of a more elaborate embodiment of the invention; and

Figures 5 and 6 are diagrams of the electrical control circuits for the form of invention shown in Figure 4.

In general, the objectives of the present invention, in its broadest aspect, are achieved by positioning a weighing scale over the mixer and employing a pneumatic conveying system in the form of a closed loop which starts and ends at a flour bin. The scale hopper is connected to the conveyer loop by a short branch line controlled by a valve which may be operated to divert flour from the conveyer line into the scale hopper. The delivery of flour to the scale hopper is stopped by Shifting the diverter valve to its straight-through position. Since there is no appreciable quantity of our in the short branch line, the valve may be controlled automatically by the tipping of the scale beam without danger of error in the weight of the delivered flour. The main conveyer then may continue to operate without cessation of flow, either for the purpose of delivering flour to other destinations or for the purpose of clearing the line by returning any flour in the line to the bin.

An air separator is associated with the scale hopper. However, in the system of the present invention, since the only flour delivered to the scale hopper is the our which is separated from the conveying air, it is not necessary to employ an efficient air separator at the scale hopper. A small rudimentary separator, which is inexpensive and requires negligible headroom, is. suicient. None of the flour which remains entrained in the air discharged from the separator is weighed.

All of the various elements of the conveying systems of the present invention are conventional and, accordingly, are illustrated diagrammatically. Similarly, standard pneumatic conveyer practice may be employed in the design and construction of the blowers, feeders, pipe lines, valves, etc. However, it has been found advantageous to employ a higher ratio of flour to conveying air than is normal practice since, with the higher flour concentrations, the small separators used operate more efficiently and the cost of constructing and operating the system is reduced. Thus, as an illustrative example, in a system in which the length of the conveying 'conduit between the feeder and the most remote destination (disregarding the return line) is forty-five feet, a pipe having an inside diameter of approximately two inches may be used to deliver two hundred pounds of flour per minute with an air lpressure at the feeder of about six pounds per square inch. A positive displacement blower which delivers approximately one hundred and fifty cubic feet of air per minute (of atmospheric pressure) may be used. As the length of the conduit increases, it is necessary to increase the air pressure, which increases the volume of air 'per pound of flour. Since it is undesirable to increase the pressure above about eight to ten pounds per square inch due to loss in efficiency and heating of the air, it is preferred to increase the diameter of the conduit if its length exceeds about one hundred feet. Thus, for a conduit one hundred and twenty-ve feet long with several bends, a three-inch conduit is preferred and will deliver two hundred pounds of flour per minute with about two hundred and sixty cubic feet of air per minute at a blower discharge pressure of about seven and a half pounds per square inch.

The system illustrated in Figure l includes a single storage bin, means for loading the bin, and means for discharging flour from the bin to either one of two mixers. In loading the bin, flour from sacks or any other source is dumped into a blender l, from which it is conveyed to the storage bin 2. From this bin, flour may be conveyed selectively to either one of a pair of our scales 3 and i mounted, respectively, over dough mixers 5 and Suitable shut-off valves 'i and 8 are provided between the weighing scales and the mixers for use in discharging the contents of the scales into the mixers after the desired quantity of flour has been delivered.

The conveying system for bin loading includes a positive displacement compressor or rblower 9, which preferably is of the Roots type and which supplies air under pressure to a three-way valve i0, which is adjustable between two positions.

For bin loading, the valve l0 is so adjusted that it connects the blower to a conveying conduit I l, which supplies air to a motor-driven paddle-wheel type feeder l2, which delivers our to the current of air owing between the conduit H and the feeder discharge conduit i3. Any suitable form of feeder may be employed for this purpose, suitable types being disclosed, for example, in the patents to Rieth No. '717,926 and Colburn No. 2,550,781. The our is conveyed by the air current through the conduit i3 and is discharged tangentially into an air separator IIS, which is simply a relatively low cylindrical housing having a coverplate provided with an axially-located air discharge opening. The bottom of the cylindrical housing is open and permits the flour to fall by gravity into a motor-driven sifter l5, which is positioned on top of the storage bin and discharges the sifted iiour :by gravity into the bin. The storage bin preferably is provided wit'h a motor-driven level bar of conventional construction. This bar, which is not illustrated in the drawings, is rotatable on a vertical axis and is positioned near the top of the bin, so that it will distribute flour evenly and lpermit complete lling of the bin.

A dust separating system is provided for removing any residual fine particles of flour from the air discharged by the separator M. This includes a centrifugal separator it, preferably of the type known by the trade-name Roto-Clone, having an air lter il connected to the air outlet thereof. The Roto-Clone separator and i'llter are connected to a main dust collecting conduit i8, which is provided with a branch conduit 2D to the central or axial opening in the top of the separator lli. The Roto-Clone separator acts not only as a separator but also as a centrifugal pump which sucks air through the dust collecting conduit i3 and thus facilitates discharge of air from the separator ld.

When it is desired to discharge flour from the bin 2 to either of the mixers, the three-way valve i6 is shifted to connect the motor-driven blower 9 to conduit 2i, which supplies air under pressure to a bin discharge feeder 22, similar in con struction to the previously described feeder l2. rThe flour-laden air leaves the feeder 22 through a main `conveying conduit 23, which extends past and closely adjacent to the flour scales 3 and Il. A pair of three-way valves 2d and 26, positioned in the conduit 23, operates in one position of adjustment to connect the conduit 23 to .branchconduits 3e and 33, respectively. Branch conduit 3G discharges tangentially into a separator 3 l, similar in construction to the previously described separator ill. The central air discharge opening in the top of separator Si is connected by a branch conduit 32 to the dust collecting conduit IB. Similarly, the branch conduit 33 discharges tangentially into a similar separator Sil, positioned on top of the scale il. The outlet from the separator Si! likewise is connected to the dust collecting conduit by a branch conduit 35.

An important feature of the invention resides in the fact that the main conveying conduit 23 is connected by a return conduit El to the storage bin, discharging tangentially into a separator 28 mounted on top of the bin. The separator 28, which is also similar to the separator ifi, has a central air outlet connected to the dust collecting conduit by abranch conduit 2t.

The three-way valves iii, 2', and 26 may be of any desired construction. Figure 2 illustrates the preferred form of valve 24. It will be understood that valve 26 may be identical in construction and that valve IU may be the same except in the minor respects hereinafter indicated.

As shown in Figure 2, the valve includes a stationary cylindrical body 31 having at one side a pair of tubular .projections 38 and 39, which projections diverge at an acute angle as they leave the body i1 and which provide outlet openings for the valve. The body 31 is provided with a cylindrical bore 49 extending generally transversely to the tubular projections 38 and 39; and a sliding valve element 4I, having a transverse cylindrical passageway 42 formed therein, is slidable within the bore 40. The valve element 4i is provided at its opposite ends with a pair of pistons 43 and 44 for actuating the valve, these pistons being connected to valve element 4| by studs 45 and 4B. The valve is operated .pneumatically or hydraulically by iluid admitted through a pair of conduits 41 and 48 connected to the ends of the cylindrical body. These conduits are controlled by a four-way valve 49, having a pressure inlet connection 59 and a-n exhaust connection 5i. The valve, which may be operated either manually or by a solenoid 52, is operable in one position to connect the pressure line 50 to the conduit 48 while the exhaust line 5| is connectedL to the conduit 41; and in the other position will connect the pressure line 50 to the conduit 41 and the exhaust line 5l to the conduit 48.

In the preferred arrangement, pressure is maintained in the line 41 when the solenoid 52 is de-energized and thus the valve normally occupies its straight-through position, which, in the case of valves 24 and 26, permits straightthrough flow and blocks the branch conduits 30 and 33, respectively. When the solenoid is energized, the valve 49 shifts, thereby applying pressure to the line 49 and connecting the line 41 to exhaust. This shifts the main conveying valve to its diverting position.

The conveying valve l0 may be identical to the valve illustrated in Figure 2 and is provided with a limit switch 54 having an operating element 55 which is engaged by the cylindrical projection 53 on the movable valve element 4| when the latter moves into the position illustrated in Figure 2. The switch 54, as hereinafter set forth in greater detail, is a double throw switch which closes one circuit when the switch is shifted by engagement with the projection 53 and opens that circuit and closes another when the valve shifts to its diverting position. In the embodiment of the invention shown in Figure 1, valves 24 and 26 are not equipped with the limit switch 54.

The principal elements of a suitable electrical control circuit for the system are diclosed diagraminatically in Figure 3. The circuit is illustrated in a parallel line diagram between the electrical supply lines 55 and 56. It consists in two main parts selectively energized by a limit switch 54, which switch is actuated by the manually-operated valve i0. When the valve is in the position in which it connects the blower 9 to conduit il for loading the bin, the switch occupies the position shown in the drawings, in which it connects line 58 to a line 59. When valve lil is shifted to the position in which it connects the blower 9 to conduit 2l for delivering flour to one of the scales 3 or 4, switch 54 breaks the connection between lines 58 and 59 and connects line 52 to line 69. The valve l0 may correspond to valve 24 shown in Figure 2 except that the operating control valve corresponding to valve 49 of Figure 2 will be manually operated 6 and switch 54 is associated with valve I0 in the manner illustrated in Figure 2.

Line 59 supplies parallel lines 5i and 62, which are connected in series with three parallel relay coils A, B and C and with ve normallyl closed,

series-connected overload switch contacts 63, 54, 65, 65 and 61, hereinafter described in greater detail. Line 9i contains a normally open, manually-operated starting switch 68. Line $2 contains in series a normally closed, manually-operated stop switch E39; a normally closed bin safety switch 18; and a normally open contact Al of relay A. The safety switch is mechanically opened by any suitable means (not shown) in the event that the bin is over-filled. Relay A also has a normally open contact (not shown) in the circuit of a motor which drives a bin leveling bar of conventional construction within the bin 2. This bar merely rotates in a horizontal plane near the top of the bin to spread flour evenly and thus permit complete nlling of the bin. Relay B has a normally open contact (not shown) in the circuit of the motor which drives the blender feeder i2. Relay C has a normally open contact CI in line 'il which extends from the main line 55 to line Si at a point between overload contacts 64 and 55.

The line 1l contains the coil of the sifter starting relay D, which has a normally open contact (not shown) in the circuit of the motor which drives the sifter l5. Line 12 extends from main line 55 in series through a pair of parallel, normally open contacts C2 and HI of the relays C and H, respectively, and the coil of the blower starting relay E to line 8i at a point between contacts 65 and 96. Relay coil D has a holding circuit through line 13 which contains the normally open contact DI of relay D and also a pressure operated switch 14 associated with the outlet of blower 9 and effective to close a normally open contact in line 13 when the blower discharge pressure increases to a predetermined value (for example, five pounds per square inch) and to open the contact when the pressure drops below a slightly lower value (for example, four pounds per square inch). The pressure at which the switch 14 opens is set at a value less than the lowest value which will exist when either of the two conveying lines contains any flour, one of the two lines being from feeder i2 to separator I4 and the other being the line from feeder 22 through lines 23 and 21.

Due to the connecting line 15, the portion of line 13 which contains the pressure-operated switch 14 also acts as a holding circuit for the blower starting relay E, which has a normally open contact (not shown) in the circuit of the motor for the blower 9. As a result, once the blower is started, the relay E will be ole-energized and thus stop the blower only after the conveying lines are cleared of flour. Likewise, if the sifter is started, both the sifter and blower will continue in operation until the line i3 is clear of flour because the pressure switch acts as a holding circuit for both of the relays D and E.

During bin loading, the blower starting relay F. will be energized by relay contact C2. At the same time, relay contact Ci starts the sifter. When the blower starting` relay E is energized. its normally open contact El in the line energizes the Roto-Clone starting relay I, which contains a normally open contact (not shown) in the motor which drives the Roto-Clone separator I6. Relay I also has a normally open ccntact Il in a parallel holding line 11, with the result that, once started, the Roto-Clone remains in operation until the stop switch 'i8 is opened manually.

The bin discharge control circuit includes the previously mentioned line Se from switch 555, which line supplies four parallel lines le, B, 8l and 82. Line 66 includes the normally closed emergency stop switch S3. Line 'i5 includes in series, a starting switch Bt, a normally closed contact GI of a relay whose coil is in line Si and the coil of a relay F. Line 3E! contains, in series, a mercury switch 35, a normally open contact Fi of relay F, and solenoid 52 of air valve ile. Line .8l contains, in series, a starting switch 8S, a normally closed Contact F2 of relay F, and the coil of relay G. Line $2 contains, in series, a mercury switch 81, a normally open contact G2 of relay G, and the solenoid 88 of valve 25. The bin discharge circuit also includes the bin discharge feeder starting relay H, which contains a normally open contact (not shown) in the circuit of the electric motor that drives the feeder 22. Re lay H is connected in a line 59 and is energized by closure of either one of a pair of normally open contacts F3 and G3 of the relays F and G. It will be noted that the lines 'it and 8G are connected to main line 55 through the overload safety contacts t and tl.

The mercury switches 25 and 8l are mounted on the beams of the weighing scales 3 and "-2 respectively, in such a manner that they normally are closed but each will break its circuit when its beam tips incident to the delivery of the desired weight of flour to the scale. These switches 85 and 8S provide holding circuits for relays F and G, respectively, through line 9d, which connects lines i9 and 3Q, and line 9i, which connects line Si and 92.

The overload safety contacts 63 to tl, inclusive, are normally closed contacts of overload relays (not shown) associated with main circuits of the motors used to drive the system; and they are so arranged that they protect the system against damage. Thus, contact 63 opens only when the motor for the bin leveling bar is overloaded; contact ti opens only when the motor for the blender feeder l2 is overloaded; contact 'Gli opens only when the motor for the sifter is overloaded; contact t opens only when the motor for the Roto-Clone separator is overloaded; and contact Bi opens only when the motor for the blower is overloaded. In addition, line B9 for the bin feeder starting relay H contains a normally closed contact S2 of an overload relay (not shown) in the main circuit of the blower motor and 'thus operates to break the circuit through line t@ when the blower motor is overloaded.

The operation of the electrical control system illustrated in Figure 3 is as follows:

When it is desired to load the bin, valve Hi is shifted, manually or otherwise, to the position in which it connects the blower to conduit i l, thus placing switch Eid in the position illustrated in Figure 3. When the starting button et is closed momentarily, relays A, B- and C are energized and are held energized thereafter by the closure of relay contact A! in the holding circuit t2. Relay A starts the bin leveling bar motor. Relay B starts the motor for blender feeder l2, thus delivering flour to conduit i3. Relay C closes contacts CI and C2, thus energizing relays D and E, which start the sifter motor and the blower motor, thereby starting the delivery of flour to the bin. Closure of contacts El in line 'i8 starts the Roto-Clone separator.

Delivery of our continues until it is stopped,

8 either manually orautomatically, in any one of the following ways:

1. Opening stop switch 69 manually will deenergize relays A, B and C, which stops the bin leveling bar and the blender feeder l2, but the sifter and blower will continue in operation until stopped by opening of the pressure switch 'M after line I3 is cleared of flour.

2. If the bin is completely filled, switch I0 will open and stop the system in the same manner as will operation of the stop switch 69.

3. If either the leveling bar motor or the blender feeder motor is overloaded, contacts 63 or 64 will open and the system will stop in the same manner as when the stop button 69 is operated.

4. If the sifter motor is overloaded, contact 65 opens and the system will stop in the same manner as before except that the sifter also will stop instantly. However, as before, the blower will clear the conduit I3 before stopping.

5. If the motors for the Roto-Clone or the blower are overloaded, the entire system will stop immediately, even though the flow conduits are not cleared. This is the only situation during bin loading in which the Roto-Clone stops or the blower stops before clearing the conduits.

For discharging our from the bin, valve l0 is shifted to the position in which it connects the blower to conduit 2l. This shifts switch 54 to break the circuits to relays A, B and C, and connects line 53 through line t@ to the line '19, B, 8l and 82. Delivery of flour is then initiated by closing either one of the switches 84 and 86 momentarily, switch 811 being closed when it is desired to deliver flour to mixer 5 and switch 86 for delivery to mixer 6. The scale of the selected mixer previously has been set, so that the beam will tip when it receives the desired weight of flour.

Closing switch 84, for example, energizes relay F, thus opening contact F2 in line 82 and disabling switch 8S. Relay F closes contact Fl, thus establishing a holding circuit for relay F through mercury switch 85 and the connecting line 90 and also energizing solenoid 52 of air valve 49. This shifts the flow valve 24 to the position in which conveying conduit 23 is connected to conveying branch conduit 30 leading to the separator 3l over scale 3. As long as relay F is energized, it is impossible to initiate delivery to the other scale d by pushing starting switch 8S.

The contact F3 of relay F closes and energizes the bin feeder starting relay H, thus starting the bin feeder 22; and contact Hl of relay H then closes and energizes the blower starting relay E. Contact E I of relay E then closes and energizes the Roto-Clone separator starting relay I, which pulls in its holding contact Il. Delivery of fiour thus begins and continues until the scale beam tips and breaks the holding circuit through mercury switch 85. This de-energizes solenoid 52 and causes the diverter valve 2li in the our conveying line to return to its straight-through position, shown in Figure 2. At the same time, relay F is de-energized, which opens contact F3 and stops the bin feeder 22.

When the diverter valve 24 is shifted to its straight-through position, conduit 23 is full of iour. However, the blower starting relay will remain energized through the pressure operated switch I4 until the blower outlet pressure drops incident to a clearing of the conveying conduits by a return of the flour through the conduits 25 and 21 to the bin. After the conveyor conduits 9 are cleared, the blower stops; but the Roto- Clone separator continues to operate until stopped by operation of the stop button 18.

Delivery to scale 4 can be effected in a similar manner by closing starting switch 86.

If it is desired to stop the delivery before the scale beam tips, this can be done by opening stop switch 83.

If the motor for the bin discharge feeder 22 is overloaded, contact 92 will open and stop the feeder by de-energizing relay H. This opens contact Hl but the blower starting relay will remain energized through pressure switch 14 until the conveying conduits are clear of flour. Overloading of the motor for the blower or for the Roto-Clone separator will open contacts 65 or 61 and stop the whole system.

A further and more elaborate improvement of the invention is illustrated diagrammatically in Figure 4. In this system, flour may be stored in four diffrent bins and flour may be conveyed selectively from any one of the four bins to any one of three mixers. Thus, as shown in the drawings, the system includes flour storage bins |02, |03 and |04 and three mixers |05, |06 and |01. The three mixers are equipped with superimposed weighing scales |00, |09 and ||0, respectively, which may discharge by gravity into the mixer on operation of shut-off valves ||I, ||2 and ||3.

The bin loading portion of the system includes a motor-driven blower ||4, which may be of the Roots type and which is connected by conduit to a paddle-type feeder ||1 associated with a blender H0 into which sacks of flour may be dumped. The feeder |1 is a motor-driven paddlewheel type of conveyer similar to those employed in the system of Figure l. The mixture of flour and air discharged by the feeder ||1 is conveyed through a main bin loading conduit |8, which runs to storage bin 4. Branch conduits |20, 2| and |22 connect the main bin loading conduit to the storage bins |0|, |02 and |03. Thus, for example, branch conduit |20 discharges tangentially into a cylindrical separator |23 associated with storage bin |0l, and branch conduits |2| and |22 and the main loading conduit ||8 similarly discharge into separators |24, |25 and |26 associated with the bins |02, |03 and |04.

It will be noted that the separators |23 to |26, inclusive, do not have axial air discharge openings, such as were provided in the separators employed in the system of Figure 1. On the contrary, the separators employed on the storage bins in the system of Figure 4 are merely cylindrical tanks having a fiat closed top and open at the bottom, so that they may discharge both the air and the our into the sifters |21, |28 and |29 associated with bins |0|, |02 and |03, respectively; and, in the case of separator |23, discharging directly into the storage bin |04. Thus, both the air and the flour are carried through the sifters and the air is discharged from the storage bins through air outlets equipped with filters |30, |3| |32 and |33. It will be noted that the filter |33 associated with bin |04 is connected to the bin by a conduit |34, whereas the remaining filters are mounted directly on the bins.

The smallest bin, |04, is intended for use with whole wheat or rye flour, and for that reason is not equipped with a sifter. Each of the storage bins, other than bin |04, is equipped with a motordriven leveling bar (not shown), similar in ccnstruction to the leveling bar incorporated in the system of Figure l, thus insuring that the bins may be completely lled level. Bin |94, because of its small diameter, requires no leveling bar. Three-way valves |35, |36 and |31 are positioned in the main bin loading conduit I8 and control communication with the branch conduits |20, |2| and |22. These valves, which preferably are similar in construction to the valve shown in Figure 2, normally occupy their straight-through positions in the main conduit |8, as indicated by the arrows on the valves in Figure 4. In this position, the branch conduits are blocked. However, each valve may be shifted to a position in which it connects the main conduit to the branch conduit and blocks communication to that portion of the main conduit beyond the valve.

lt will be apparent that, by manipulating the conveying valves |35, |35 and |31, flour may be delivered from the blender to any one of the three storage bins and that the flour delivered to the bins |0|, |02 and |03 is sifted before it is deposited in the bins.

The bin discharge portion of the system shown v in Figure 4 includes a motor-driven Roots type blower |38, which discharges into a main air supply line |39, which is connected to a motor-driven paddle-type feeder |40 positioned beneath the storage bin |0|. Branch conduits |4|, |42 and |43 connect the air supply line |39 to motordriven paddle-type feeders |44, |45 and |46 associated, with the storage bins |02, |03 and |04, respectively. Diverter valves |41, |40 and |49 are positioned in the air supply conduit |39 for connecting that line to the branch conduits |4|, |42 and |43, respectively. These diverter valves, which preferably are similar to the valves shown in Figure 2, normally occupy the straight-through position shown in Figure 2, in which air is directed through the conduit |39 to feeder |40, as indicated by the arrows on the valves in Figure 4. However, any one of these valves may be shifted to a position in which it diverts air to its associated branch conduit and blocks communication with the main air conduit beyond the Valve.

The mixture of air and flour which leaves feeder |46 is delivered to a main conveying conduit |50, which extends past the flour scales |08, |09 and ||0. In the vicinity of the scales, the main conveying conduit |50 is provided with three diverter valves |5|, |52 and |53, which may be similar in construction to the valves shown in Figure 2. These three valves normally occupy their straight-through positions, in which they block communication to branch conduits |54, |55 and |5|3` leading, respectively, to separators |51, |58 and |59 mounted on the scales |08, |09 and I0, respectively. However, when shifted to their diverting positions, the valves connect the main conveying conduit 59 to the branch conduit associated with the valve and block communication with the main conveying conduit beyond the valve.

The main conveying conduit |50 is connected to the feeders |40, |44 and |45 by branch conduits |60, ||i| and |62 and diverter valves |63, |64 and |65, respectively. Diverter valves |63, |64 and |65 normally occupy their straightthrough position, which establishes the connections indicated by the arrows in Figure 4. These valves are similar in construction to the valves shown in Figure 2. It should be noted, however, that they are reversed in position so that they always discharge through the boss 53 of the valve shown in Figure 2 and may receive the air and flour mixture from either of two conduits. Thus, in the case of valve |53, for example, conduit 200 will be connected to the tubular projection on the valve housing and the main conduit |50, at the point at which it enters the valve |03, will be connected to the tubular projection 30 on the valve housing. Valve |60 is similarly arranged. In the case of valve |65, conduit |62 is connected to the tubular projection 30 and the entering main conduit connection is made through the tubular projection 39 of the valve housing. As a result of these diverter valves, it is possible to connect any one of the feeders |40, |44, or |30 to the main flour conveyer conduit |50.

The main conveying conduit |50, at a point beyond the last scale 'diverter valve |53, is connected to a return conduit |66, which, in turn, eX- tends past the four storage bins, terminating at a separator 51 mounted on storage bin |0|.

Branch conduits |68, |09 and |10 connect the return conduit to separators |10, |1| and |12 mounted, respectively, on the storage bins |02, |03 and |04. Diverter valves |13, |14 and |15 connect the return conduit |66 to the branch conduits |68, |59 and |10 and normally occupy their straight-through positions, in which they connect to separator |61 on bin |0| and block communication between the return conduit |66 and the branch conduits. These valves, however, which also are similar to the valve shown in Figure 2,

may be shifted to connect any one of the branch f conduits to the return conduit |66 and block off communication with the return conduit beyond the Valve.

The separators |61, |10, |1| and |12 are similar in construction and operation to the separators |23, previously described. It will be noted, however, that on storage bin |04 the two separators |26 and |21 are superimposed and, in effect, constitute a single separator, which is merely a cylindrical tanklike structure, closed at the top and having two tangential inlets.

A dust collecting system is provided in connection with the separators on the flour scales. This system includes a Roto-Clone separator |16 and associated filter |11, which are connected by a dust conduit |18 to the air outlet of the separator |50 on scale H0. Branch conduits |19 and |60 connect the air outlets of separators |51 and |50 to the dust conduit |18.

Any suitable means may be provided for controlling the system during bin loading, one suitable form of electrical control circuit being illustrated diagrammatically in Figure 5. As there shown, the control circuit is connected between a pair of electrical supply lines |90 and |9| cludes a line |92, containing, in series, a normally open starting switch |93, the coil of relay J, and eight normally closed overload safety switch contacts |03 to 20|, inclusive. Line |32 has a parallel branch 202, containing, in series, a normally closed stop switch 203, the normally open contact J of relay J, the normally open contact T| of a relay T, and the coil of a relay K having a normally open contact (not shown) in the main circuit to the motor which 'drives the blender feeder ||1. A connection 204 between lines |02 and 202 completes a holding circuit for relay J through the stop switch and relay contact J l.

The circuit also includes a line 200, containing the normally open contact J2 of -relay J and a selector switch 206 which can complete a circuit through any one of lines 201, 208, 200 and 2|0. Lines 201, 200 and 209 contain the solenoids 2| 2|2 and 2 I3, respectively, of the air valves which control the conveyer diverter valves |35, |36 and It in- 12 |31. These solenoids correspond to the solenoid 52 of Figure 2 and, when energized, shift the valves to diverting position, thus delivering flour to one of the associated branch lines |60, |6| and |62. Line 2 0 contains the coil of a relay L.

The circuit also includes a branch line 2M extending from line 205 and which supplies current to three parallel lines 2 |5, 2|6 and 2 |1. Line 2|5 contains a normally open limit switch 2l0 associated with diverter valve |35 and a pair of parallel connected coils of relays M and N. Limit switch 2|8 corresponds to switch 50 of Figure 2 and is open when the valve |35 is in its straightthrough position. Relay M controls sifter |21 and has a normally open contact (not shown) in the main circuit of the motor which drives sifter |21. Relay N controls the leveling bar in bin |0| and has a normally open contact (not shown) in the main circuit of the motor which drives that leveling bar. Line 2|6 contains a similar normally open limit switch 2|9 associated with diverter valve |36 and a pair of parallel connected coils of relays O and P. Relay O controls sifter |28 and has a normally open contact (not shown) in the main circuit of the motor which drives that sifter. Relay P controls the leveling bar in bin |02 and has a normally open Contact (not shown) in the main circuit of the motor which drives that leveling bar. Line 2|1 contains a similar normally open limit switch 220 associated with diverter valve |31 and a pair of parallel connected coils of relays Q and R. Relay Q controls the sifter |20 and has a normally open contact (not shown) in the main circuit of the motor which drives that sifter. Relay R controls the leveling bar in bin |03 and has a normally open contact (not shown) in the main circuit of the motor which drives that leveling bar. Because of its smaller size, bin |04 has no leveling bar.

Lines 2|5, 2|6 and 2|1 also may be energized by a line 22|, which contains a normally open contact Sl of a relay S. This line 22| also acts as a holding circuit to energize line 205 after relay J is de-energized.

The circuit includes a line 222, which may be energized by any one of the parallel normally open contacts LI, Nl, Pl and Rl of relays L, N, P and R, and, when energized, supplies current to parallel lines 223, 224 and 225. Line 223 contains the coil of relay S which controls the compressor ||4 and contains a normally open contact (not shown) in the main line of the motor which drives the compressor. Relay T has a normally open contact in line 202, as previously mentioned, and hence indirectly controls the blender feeder H1. Line 225 contains a signal light 226, which indicates to the operator that a bin loading operation is in progress.

Line 222 also may be energized by a holding circuit through a line 221 containing a pressureoperated switch 228 associated with the air outlet from blower l l0. The pressure switch, which is a standard commercial item, is set to close the circuit through line 221 when the pressure of the air discharged by blower ||l reaches a predetermined value suicient to convey our to the closest destination, i. e., bin |0|, and to open the circuit when the pressure drops incident to a substantially complete clearing of flour from the conveying conduits. This switch keeps the compressor running after the stop button 203 breaks the circuit through relays J and K until after the flour lines are clear. Moreover, it keeps all of the rest of the circuit lenergized through contact Sl of relay S. As a result, when the 13 stop button is depressed, the blender feeder ||1 stops but the blower continues to run, as well as the sifter and leveling bar of the bin to which delivery is occurring, and the diverter valve does not return to its straight-through position until the conveying conduit is cleared.

In order to eiect delivery to any desired bin, the'selector switch 20B is moved to the appropriate contact in one of the lines 201 to 2|0, inclusive. Lines 201 to 209, which control bins to |03, respectively, operate, when energized, to lshift the associated diverter valve |35, |36, or |31. If bin |04 is selected, no valve is operated but relay L is energized. The diverter valves, in turn, close limit switches 2|8, 2|9 and 220, respectively, which, in turn, energize the relays which start the sifter and leveling bar in the selected bin. The starting relays N, P and R for the leveling bars (or the relay L when bin |04 is selected) energize line 222 and thus start the compressor and also energize relay T, which closes contact T| and thus energizes the starting relay K for the blender feeder ||1. When thus started, the system delivers iiour to the selected bin until stopped by de-energization of relays J and K. This can be done by manipulation of the stop button 203 or will result automatically if any one or more of the safety overload contacts |94 to 20|, inclusive, open the circuit through line |92.

The safety overload contacts are normally closed contacts associated with overload relays, the coils of which (not shown) are connected in the main lines to the drive motors of the system, and each operates to open its contact when the associated motor is overloaded. Contact |94 is controlled by the circuit of the motor for blender |1; contact |95 by the motor circuit for the compressor ||4; contact |96 by the motor circuit for sifter |21; contact |91 by the motor circuit for the leveling bar in bin |0|; and contacts |98 to 20|, inclusive, are controlled, respectively, by the circuits of the motors for the sifters and leveling bars associated with bins |02 and |03. It will be noted that, in the case of an overload on the motors of the sifter, leveling bar or compressor, the system will clear the conveyer conduit of flour before shutting down these three units. Damage to the motors can be avoided by setting the overload contacts to open at an overload which the motors can carry for the brief interval required to clear the lines.

The primary portions of the preferred electrical circuit for controlling delivery of ilour from any one of the four bins to any oney of the three mixers are illustrated diagrammatically in Figure 6. As there shown, the circuit is supplied with electricity by power lines 240 and 24|, between which extend the main circuit lines 242 to 250, inclusive.

Line 242 is the overload safety control circuit which operates to stop the system by a desired sequence of operations in the event of motor overloads. Line 242 contains the coil of a relay a, the normally closed contact ml of a relay m, and live normally closed overload safety contacts 25| to 255, inclusive. The contacts 25| to 254, inclusive, are normally closed contacts of overload relays the coils of which (not shown) are connected in the main circuits of the motors which drive the bin discharge feeders |40 `to |46, respectively. Contact 255 is controlled by a similar overload relay coil (not shown) in the main circuit of the motor which drives compressor 14 |38. Each of these relays opens its contact in the event that the motor with which it is associated becomes overloaded. A normally open contact kl of a relay k is connected in parallel with Contact ml and serves to energize line 242 when relay lc (described hereinafter) is energized, even though Contact ml is open. It will be noted that, when the system is in its inoperative or idle condition illustrated, the coil of relay a is energized as soon as the main power switch (not shown) is closed to energize lines 240 and 24| andV will remain energized under all normal conditions of operation.

Lines 243, 244 and 245 are the scale selector circuits which control the destination of the delivered our and also determine the amount which is received by the selected destination. All of these circuits are completed through the normally open contact al of the relay a. Under all normal operating conditions, contact al is closed because relay a is energized. The lines 243, 244 and 245 contain normally open starting switches 256, 251 and 258, respectively, and also the coils of relays b, c and d, respectively. Line 243 has a parallel line 259 containing a normally closed mercury switch 260 that is mounted on the beam of scale |08, a normally open contact bl of relay b, and also a solenoid 26| of the solenoid air valve which, when energized, shifts the diverter valve |5| to its diverting position. The mercury switch 260 is so positioned on the scale beam that, when the beam tips incident to the receipt by the scale hopper of the weight of flour for which the scale is set, the switch breaks the parallel circuit 259. Since the starting button 255 will remain closed only momentarily, a holding circuit for solenoid 26| is provided through mercury switch 260 and contact bl, and this circuit also holds the coil of relay b energized due to the connecting line 262.

Lines 244 and 245 have branch lines 263 and 264, which contain similar normally closed mercury switches 265 and 256 mounted, respectively, on the beams of scales |09 and ||0; and the branch lines also contain, respectively, normally open contacts c2 and d3 of the relays c and d and solenoids 261 and 268 of the solenoid air valves which shift the diverter valves |52 and |53, respectively, to their diverting position when their solenoids are energized.

As a result of the above-described circuits, any one of the diverter valves |08, |09 and ||0 may be shifted to its diverting position and will remain in that position until its main control line 243, 244 or 245 is broken. Emergency stop switches 269, 210 and 21| are provided in the lines 243, 244 and 245, respectively, so that any one of these lines may be broken at any time and thus rie-energize the related valve solenoid and stop delivery of iiour to the associated scale hopper. The circuits 243, 244 and 245 also will be broken by contact al in the event that any of the above-mentioned motors is overloaded and thus open one of the safety overload contacts in line 242.

Once one of the starting switches 256, 251 and 258 is closed momentarily, the associated line will remain energized until the selected scale hopper receives the desired weight of flour and then will be de-energized by opening of the mercury Conventional interlocking relay contacts are provided to prevent the energization of any one of the scale selector control lines 243, 244 and 245 while another is energized. Thus, line 243 contains the normally closed contacts cl and dl of relays c and d; line 244 contains the normally closed contacts b2 and d2 of relays b and ci; and line 245 contains the normally closed contacts 193 and c3 of relays b and c. This prevents the selection of one scale hopper during delivery of iiour to any other. As will be pointed out hereinafter, the relay contacts ml and ici also serve to prevent selection of a scale for receipt oi ilour during the period after completion of one delivery that is required to clear the conveyor line of flour.

In addition to making a selection of the destination icy depressing one of the start buttons 256, 2"7 and 250, the operator must also select the bin from which our is to be drawn. This is done by shifting a tandem bin selector tap switch having a pair of mechanically connected contact arms 272 and 273, which arms are electrically connected to line 247. Switch arm 272 is adapted to make contact with any one of four contacts 275, 275, 276 and 277, which correspond, respectively, to the bins |i| to |04, inclusive. Switch arm 273 is adapted to make contact with four contacts 278, 270, 280 and 28|, which similarly correspond to the four bins. The arms move together and hence always engage one contact in each group.

The line 247 to the bin selector switch is energized oy closure of a normally open contact el of relay e, which, in turn, is energized by the scale selector circuits through a series of relay contacts and limit switches in line 246. Thus, line 246 contains, in series, the normally open contacts b4, c4 and d4 of relays b, c and d, and each of these contacts is connected in parallel with a pair of contacts in a limit switch associated with one of the scale diverter valves |5|, |52 and |53. The limit switch 282 is associated with the diverter valve |5| for scale |68 and corresponds to the limit switch 54 of Figure 2 except that it is a double throw switch. When lthe valve 75| is in its straight-through position, the switch contact 202 occupies the solid line position shown in Figure 5 and thus bridges the otherwise open circuit at relay contact b4. When valve |5| is shifted to its diverting position, the contact of switch 262 occupies the dotted line position shown in Figure 6 and closes the circuit through line 246 and relay coil e. Scale diverter valves |52 -anol |53 are equipped with similar limit switches |83 and |64, respectively, which are associated with the respective relay contacts c4 and d4 in line 246 in the same manner as limit switch |62 is associated with contact b4.

As a result of this arrangement, energization of relay b by start button 256 will not energize relay e until after the diverter valve |5I has shifted -to its diverting position; but subsequent de-energization of relay b will immediately deenergize relay c, even though diverter valve |5| for some reason fails to return to its straightthrough position. The same result occurs in the event of operation of valves |52 or |53. More important, if any one of the three scale diverter valves |5|, |52 and |53 is out of its straightthrough position, it is impossible to energize relay e by operating the start button which controls one of the other scale diverter valves.

Arm 272 of the loin selector switch controls the energization of lines 285 to 293, inclusive, which contain, respectively, the solenoids 294 to 302, inclusive, that actuate the air control valves of the diverter valves, as follows: solenoid 294 controls valve |63; solenoid 205 controls valve |64; sole noid 296 controlsI valve |47; solenoid 297 controls valve |73; solenoid 296 controls valve |42; solenoid 29B controls valve |74; solenoid 300 4controls valve |49; solenoid 30| controls valve |55; and solenoid 302 controls valve |75. The arrangement is such that, when the solenoids 264 to 302 are de-energized, the controlled diverter valves are in their straight-through positions, in which llow may occur through the valves in the directions indicated by the arrows in Figure fi. If any solenoid is energized, its associated valve is shifted to its diverting position. These solenoids correspond to the solenoid 52 in Figure 2.

It will be noted `that solenoid 264 is energized when switch arm 272 engages contact 274, thus shifting valve |63 to the position in which flour may be delivered from bin |05 solenoids 295, 296 and 297 are energized when switch arm 272 engages contact 275, thus shifting valves |64, |41 and |73 into the positions in which flour may be delivered from bin |02; solenoids 263 and 299 are energized when switch arm 272 engages contact 276, thus shifting valves |48 and |74 into the position in which flo-ur may be delivered from bin |63; and solenoids 366, 30| and 302 are energized when switch arm 272 engages contact 277, thus shifting valves |40, |65 and |75 into the positions in which flour may be delivered from bin |04.

Contact 278 of the second switch arm is connected to a line 303, which contains three normally closed limit switches 304, 365 and 3:76 and the coil of a relay f. Limit switches 304, 305 and 306 are associated, respectively, with diverter valves |73, |74 and |75 in the same manner as limit switch 54 is associated with the valve shown in Figure 2. They are so constructed that they are closed when their associated valves are in the straight-through position. Accordingly, switch 304 is open when flour is drawn from bin |02;

switch 395 is open when flour is drawn from bin contacts 219, 2st and zal of switch arm 213v are connected by lines 307, 309 and 305 to line 303 at points positioned, respectively, beyond the switches 304, 305 and 306. Accordingly, the coil of relay f is energized at anytime current is supplied to switch arm 273 unless one of the valves |73, |74 and |75 is in an improper position. Since relay f has a normally open contact fl in line |46, which supplies current to the starting relays g, h, i and 7 for the bin feeders |40, |44, |45 and |46, this arrangement prevents the feeding of flour to the conveyer in the event that one of the valves |73, |74 and |75 is in an improper position. The previously-mentioned relay e also contains a normally open contact e2 in the line |48, and this insures that no flour will be fed to the conveyer if any one of scale ,diverter valves |5|, |52 and |53 is in an improper position. As a further insurance that `the remaining diverter valves will be properly positioned, limit switches associated with the valves which must be shifted to effect delivery from any bin are connected in the line which contains the coil of the bin feeder starting relays for that bin. Thus, line 3|9 for the -coil of the starting relay g for bin feeder |40 contains a normally open limit switch 3|4, which is associated with valve |63. When valve |63 is 17 shifted lto connect conduit |60 to conduit |50, as is necessary to withdraw flour from bin |I, limit switch 3 I4 closes. The line 3| for the coil of the starting relay h for bin feeder |44 contains similar normally open limit switches 3 5, 3 I6 and 3 I 1,

which are associated, respectively, in like manner with the diverter valves |41, |64 and |13, whi-ch must be shifted to withdraw flour from bin |02. Line 3 l2, which contains the coil of starting relay i for bin feeder |45, contains similar normally open limit switches 3|8 and 3|8, which are associated, respectively, with diverter valves |48 and |14; and line 3|3 for the starting relay y' for bin feeder |46 contains the normally open contacts of limit switches 320, 32| and 322, which are similarly associated with diverter valves |49, |65 and |15, which must be shifted to withdraw flour from bin |04. Accordingly, the bin feeder starting relays are energized only when the diverter valves are in proper position for the selected conveying operation.

It may be noted that each of the diverter valves |13, |14 and |15 differs from the remaining diverter valves in that it is equipped with two limit switches: one a normally closed limit switch in line 303; and the other a normally open limit switch in the feeder starting relay circuits. These two limit switches may be separate switch units mounted side by side in the manner of switch 54 in Figure 2; or may be a single switch controlling a pair of circuits. Thus, for example, the switches 304 and 3|1 may be combined as one movable contact which opens the circuit through line 303 and closes the circuit through line 3|| when valve |13 is shifted to its diverting position. Limit switches 305 and 3 I 9 similarly may be combined, as may be switches 306 and 322.

The relays g, h, i and j contain normally open contacts (not shown) positioned, respectively, in the main circuits of the motors which drive the bin feeders |40, |44, |45 and |46 and thus, when one of these relays is energized, it starts the appropriate feeder. The feeder will remain in operation until relay e is deenergized by the return of one of the scale diverter valves I5|, |52 and |53 to its straight-through position. This opens contact e2 and de-energizes the feeder relays.

Line 249 contains the coil of relay k and is energized by closure of any one of the normally open contacts gl, hl, il and y'I of the bin feeder starting relays g, h, i and 7'. Relay lc, in turn, closes a normally open contact k2 in line 250 and thus energizes the coil of a starting relay Z for the compressor |38 and also a pilot light 323 and the coil of a relay m, which are connected in parallel with relay Z. As previously indicated, relay Z is energized when any one of the bin feeder starting relays is energized and it will be de-energized when the bin feeder starting relays are de-energized by return of the diverted scale valve to its straight-through position. However, the conveyor line must be cleared of flour before the compressor stops and, accordingly, the compressor starting relay is held energized by a pressureoperated switch 324, notwithstanding the opening of contact k2. Switch 324, which is similar in construction and function to switch 228 described in connection with Figure 5, is closed in response to the pressure of the air discharged by blower |38 and opens in response to the drop in that pressure which occurs when the conduits are cleared of our. This brings the system to a complete stop and returns all diverted valves to their normal positions by reason of the opening of contact Z1 of the compressor starting relay l. The scale diverter valve previously had returned to its straight-through position, thus deenergizing relay e, which, in turn, de-energized the bin feeder relays and stopped delivery of flour to the system.

During the interval between the stopping of the bin feeder, which de-energizes relay 1c, and the stopping of the compressor as the result of opening of switch 324, there is still flour in the return line, and, therefore, that our would be trapped and plug the line if one of the scale diverter valves were shifted to its diverting position as the result of operation of one of the starting switches 256, 251 and 258. This is prevented by reason of the fact that, during that interval, contacts m| and 7c| in line 242 are both open, thus de-energizing relay a and opening contact al which disables the starting or scale selecting circuits.

It will be noted that, unlike the remaining lines in the circuit, line 250 is not connected directly to the main supply line 24| but is connected only through the overload safety contact 255 in line 242. As a result of this arrangement,

' an overload on the compressor motor will stop the entire system, but an overload on any other motor will stop everything except the compressor and the compressor will hold the divertedl bin valves against shifting until after the conduits are cleared of flour. I

For convenience, each of the starting switches 256, 251 and 258 is located on the mixer which it controls, while the selector switch 212-213 may be located in a central position in the mixing room.

While only two forms of the invention are illustrated and described, it will be apparent that the principles of the invention may be embodied in a wide variety of forms. Thus, for example, the multiple bin system of Figure 4 employs a single main conveying conduit for a plurality of bins, but in some cases it may be desirable to use two main conveying conduits, one of which would run from one or more bins past a series of mixers and the other from other bins past the same mixers. This would simply involve a duplication of the more simplied form of system illustrated in Figure 1 except that each scale hopper, or at least some of them, would be supplied selectively by either of the two conveyers.

What is claimed is:

1. A pneumatic conveying system for delivering bulk flour or like material from a container to a remote destination, including a container from which material may be drawn, a weighing scale hopper at a remote destination to which material may be delivered, said hopper having a movable element which moves from its normal position when the hopper has received a predetermined weight of flour, a main conveying conduit extending in a closed loop from its inlet end at the container past the scale hopper in close proximity thereto and returning to the container at its discharge end, means including a diverter valve in the main conduit operative in its diverting position to divert material from the main conduit into the receptacle and in its straightthrough position to block communication between the main conduit and the scale hopper and permit flow through the main conduit, means for blowing air through the main conduit, means for feeding material from the container into the main conduit at its inlet end for delivery by the air flowing therethrough into the scale hopper when said valve is in di- 'aesasiv verting position, means operable in response to movement of said element from its normal position while material is being conveyed through said main conduit to shift said valve to its straight-through position in order to terminate delivery of material to said scale hopper, and means actuated in response to movement of said diverter valve to its straight-through position for stopping the feed of material to the main conduit in order to permit the air blowing means to clear the main conduit by returning the material therein to the container after the diverter valve is returned to its straight-through position.

2. A system as defined in claim 1, including mechanism for stopping operation of said blowing means, said mechanism including means to delay the stopping of said blowing means until after iiour is blown clear of the main conveyor conduit.

3. A system as dened in claim 2, including means for shifting said valve to its diverting position and means operative after the valve has been returned to its straight-through position to prevent operation of said valve shifting means until after the conveyor conduit is cleared of material.

4'. A system as defined in claim 2, including means for shifting said valve to its diverting position and starting the air blowing means and the material feeding means, and means operable on return of the valve to its straight-through position to' prevent shifting of said valve to its diverting' position until after said air blowing means has stopped.

5. A system as dened in claim l, in which a pressure responsive means operatively connected to the' air blowing means and responsive to the pressure of the air delivered by said means is provided for stopping operation of said blowing means when the air pressure drops incident to the clearing of flour from the main conveyor conduit.

6. A system as dei-ined in claim 5, including means for shifting said valve to its diverting position and means operative after the valve has been returned to its straight-through position to prevent operation of said valve shifting means until after the conveyor conduit is cleared of material.

7. A system as defined in claim 1, including means for shifting said valve to its diverting position and means operative after the valve has been returned to its straight-through position to prevent operation of said valve shifting means until after the conveyor conduit is cleared of material.

8. A pneumatic conveying system for delivering bulk ilour or like material to any one of a plurality of destinations, including a container from which the material may be drawn, a plurality of weighing scale hoppers to which it may be delivered, each of said scale hoppers having a movable element which moves from its normal position when the hopper has received a predetermined weight of flour, a main conveying conduit extending in a closed loop from the container past the vicinity of' said scale hoppers and back to the container, means including a plurality of diverter valves in the main conduit associated respectively with said scale hoppers and each operative in its diverting position todivert material from the main conduit into the associated hopper and in its straight-through position to block communication between the main conduit and the hopper and permit flow through the main conduit, means for blowing air through the main conduit, means for feeding material from the container into the main conduit for delivery by the air flowing therethrough to any scale hopper whose diverter valve is in its diverting position, means operable in response to movement of the movable element of any of said scale hoppers from its normal position While material is being delivered to such scale hopper to shift the Avalve associated with said hopper to its straightthrough position, and means actuated in response to movement of said last mentioned diverter valve to its straight-through position for stopping the feed of material into the main conduit in order to permit the air blowing means to clear the main conduit by returning the material therein to the container after the diverter valve is returned to its straight-through position.

9. A system as deiined in claim 8, including mechanism for stopping operation of said blowing means, said mechanism including means to delay the stopping of said blowing means until after flour is blown clear of the main conveyor conduit.

10. A system as defined in claim 9 including means for shifting any one of said, diverter valves to its diverting position, means operable incident to the movement of any one of said valves to diverting position to prevent shifting of any other of said valves to diverting position while said one is in a diverting position, and means operable when the air blowing means is operating to prevent shifting of any of said valves from its straight-through to its diverting position until after the main conveying conduit is clear of flour,

l1. A system as defined in claim 8, including pressure responsive means operatively connected to the air blowing means and responsive to the pressure oi the air delivered by said means for stopping 1operation of said blowing means when the air pressure drops incident to the clearing of flour from the main conveyor conduit.

l2. A system as denned in claim 11 including means for shifting any one of said diverter valves to its diverting position, means operable incident to the movement of any one or" said valves to diverting position to prevent shifting of any other of said valves to diverting position while said one is in a diverting position, and means operable when the air blowing means is operating to prevent shifting of any of said valves from its straight-through to its diverting position until after the main conveying conduit is clear of flour.

13A. A system as defined in claim 8, including means for shifting any one of said diverter valves to its diverting position, means operable incident to the movement `oi any one of said valves to diverting position to prevent shifting of any other of said valves to diverting position while said one is in a diverting position, and means operable when the air blowing means is operating to pre- Vent shifting of any of said valves from its straight-through to its diverting position until after the main conveying conduit is clear of our.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,301,168 Renkin Apr. 22, 1919 1,935,843 Goebels Nov. 2l, 1933 2,580,581 Niemitz Jan. 1, 1952 

